1. Field of the Invention
This invention relates to crab traps and, more particularly, to structures for improving the yield and ease of use of conventional crab traps.
2. Description of the Prior Art
Conventional crab traps have been used in their present form for many years. These traps have an overall shape of a right prism formed by rectangular frames rigidly spaced apart from each other by support members. The frame members support a number of rectangular net panels and an entrance tunnel through which the crab crawls to enter the trap. The entrance tunnel is formed by a first net panel extending from one frame member inwardly and terminates along the far edge of an elongated, rectangular entrance frame facing upwardly intermediate the rectangular frames. A second net panel extends from the opposite frame member and terminates along the closer elongated edge of the entrance frame while a pair of third net panels extend from the corners of the trap and terminate along opposite sides of the entrance frame. A crab enters the trap by crawling along the first panel and through the entrance frame. As the trap fills with crabs, the bait becomes completely surrounded by the crabs and it is thus inaccessible to other crabs in the trap. Consequently, many of the crabs lose interest in remaining in the trap and seek escape. It has been estimated that, for large catches, 40% to 50% of the crabs entering the trap manage to leave by crawling upwardly along the third panels to the upper side of the second panel, and then crawl along the second panel to the entrance frame where they exit onto the outer surface of the first panel.
Attempts have been made to improve the yield of conventional crab traps by preventing crabs from leaving the trap. However, all such attempts have focused on preventing the crab from exiting through the entrance frame. This approach has met with little success since these structures have the effect of deterring crabs from entering. In one of these approaches a baffle plate angles upwardly from the longitudinal edge of the rectangular opening closest to the end of the trap. The plate does not prevent the crabs from entering the trap since its inner end is spaced a sufficient distance above the opening. However, an escaping crab crawling along the inner surface of the second panel crawls along the upper surface of the plate and falls off its inner edge back into the trap. The primary disadvantage of this approach is that the plate vibrates excessively when the crab trap is placed in a current which is normally present during tide changes. This vibration has a tendency to scare the crabs so that they do not enter the trap.
Another example of the conventional approach is to pivotally mount several spaced apart retaining fingers on the entrance frame so that they cover the opening through which the crab enters the trap. The three ends of the fingers rest upon the upper edge of the frame so that they pivot upwardly as a crab passes through the opening. However, since the free ends rest upon the upper surface of the frame they cannot pivot downwardly and thus prevent the crab from passing downwardly through the opening. The principal disadvantage of this structure is that many crabs appear to be unwilling to lift the fingers from the frame in order to gain entrance to the trap. Consequently, as with the previous example of the conventional approach, a fewer number of crabs enter the trap.
Conventional crab traps are utilized to fish different species of crabs. In Alaskan waters, King and Tanner crabs are the principal species of crabs which are caught. When fishing for King crab, which is substantially larger than Tanner crab, the law requires that the netting an "escapement" end of the trap have a mesh which is large enought to allow Tanner crabs to escape. However, when that same trap is used to fish for Tanner crab, it is necessary to reduce the size of the opening formed by the entrance frame and to also reduce the size of the mesh covering the escapement end so that the Tanner crabs cannot escape.
At present, the opening formed by the entrance frame is usually narrowed by securing a board to the frame along one longitudinal edge of the frame, typically by using large rubber bands. The primary disadvantages of this approach are the down time required to convert the traps from one species to another and the tendency of the board to move away from the longitudinal edge and hence entirely block the entrace to the trap.
The relatively large mesh netting covering the escapement end of the trap is normally converted to a smaller mesh by either of two conventionally used techniques. The simplest technique is to simply tie a net over the escapement end of the trap. The second technique is to mount a rectangular frame having a smaller mesh over the escapement end of the trap. The principal disadvantage of the last mentioned technique is the need to buy, store and carry various size frames to fit various size crab traps.